This invention relates to seals and sealing and has particular reference to the sealing between a pair of relatively rotatable elements such as between a shaft and a wall through within the shaft extends. For the purposes of illustration, the invention will be described with reference to a fluid seal assembly used in the water pump of an internal combustion engine.
Rotary mechanical face seal assemblies commonly used in automotive waterpumps and similar relatively low hydraulic pressure sealing applications typically include a sealing boot of a deformable elastomeric material, a seal seat, a sealing washer, a spring for biasing the sealing washer against the seal seat, and an arrangement for retaining the components in sealing relation with respect to a stationary housing and rotating shaft passing through a bore of the housing. Rotary mechanical face seals are shown in Dornhofer U.S. Pat. No. 2,322,834, issued Jun. 29, 1943; Schmitz U.S. Pat. No. 2,474,123, issued Jun. 21, 1949; Solari U.S. Pat. No. 2,785,913issued Mar. 19, 1957; Gits U.S. Pat. No. 2,824,760, issued Feb. 25, 1958; Payne U.S. Pat. No. 2,899,219, issued Aug. 11, 1959; and Dahlheimer U.S. Pat. No. 3,554,559, issued Jan. 12, 1971, each patent being specifically incorporated herein by reference.
Oftentimes a substantial portion of the axial sealing force results from the sealing boot deflecting from its as molded free state to an as used deflected state. The force needed for this deflection normally does not actively contribute to the sealing and if needed will eventually diminish to a negligible level due to relaxation and deterioration of the elastomer. Further, the spring commonly used in these assemblies typically has a nominal spring force that is significantly higher than the minimum force required to assure proper sealing even after accommodating for normal axial tolerances of the combined components, or load tolerance in the spring, or changes in the closing force in actual service due to fluctuations in the pressure of the fluid being sealed.
A primary object of this invention is provision of an improved rotary mechanical face seal assembly containing unique features and combination of features which provide extended seal operational life by enabling the seal assembly to operate with a constant and relatively low nominal closing force regardless of the length of time in service or fluctuations in the hydraulic pressure of the fluid being sealed.
In accordance with this invention there is provided a face seal for fluid sealing between a rotatable shaft and a housing through which the shaft extends, the seal including a stationary assembly sized for fluid tight engagement to a cooperating bore in the housing and a rotating assembly securable to the shaft. In one preferred embodiment, the rotary and stationary assemblies are held together as a unit in a cylindrical casing adapted to be secured to the shaft for rotation therewithin, the rotating assembly including a seal seat mounted in a shroud formed at one end of the casing. The shroud is deformed about flats formed in the seal seat and the other end of the casing is flared outwardly to unitize the assembly and bring the parts into concentricity with one another.
The stationary assembly includes an elastomeric boot having a contoured diaphragm disposed between radially spaced annular outer and reentrant portions, an annular seal washer having a radial sealing face abutting against a like sealing face of the seal seat and an annular cavity for receiving the inner reentrant portion, a ferrule having a cylindrical body for pressing the reentrant portion against the seal washer and to lock the reentrant portion in the annular cavity, the ferrule including a radially expanding contoured skirt disposed in close supporting relation to the diaphragm and forming a first spring seat, a cup-shaped spring retainer fixedly supported about its circumference to the inner wall of the boot outer portion, the spring retainer including an annular U-shaped portion disposed in closed supporting relation to the diaphragm and a second spring seat, and a spring supported and compressed between the spring seats for biasing the ferrule and seal washer axially against the seal seat. The seal washer is preferably integrally molded of a phenolic plastic or of sintered carbon graphite, and also of a resin bonded carbon. The seal seat is preferably of ceramic or silicon carbide and supported in compression by an O-ring to inhibit cracking such as by thermal shock.
In one particular aspect of the seal herein, the annular outer portion of the boot is of thickened construction and integrally molded about a specially configured tabular insert having end flanges (or tabs), respectively, directed radially inwardly and outwardly. These flanges advantageously position the boot in the bore and the spring relative to the boot.
Further, a specially configured washer-shaped insert is integrally molded into the seal washer, the insert having angularly spaced lands disposed about a nonsealing face. Such composite seal washer has a nose portion spaced from the diaphragm and provides a means for extracting dissipating frictional heat from the sealing surface and/or interior of the seal washer and transmitting it directly to the fluid being sealed.
In yet another aspect herein interengageable fingers and recesses lock the spring seat and ferrule together in a manner which permits relative axial and minor angular movement therebetween.
An advantage of the above seal assembly is provision of a construction wherein the contoured diaphragm portion of the elastomeric boot is used in virtually the same shape in which it was originally molded such that only the spring force is necessary to bias the seal washer against the seal seat. The spring acts through the spring seats of the spring retainer and ferrule to provide virtually all of the mechanical axial closing force of the seal washer against the seal seat with virtually none of the closing force being contributed by deflection of the contoured diaphragm. The diaphragm neither effectively adds to or subtracts from the loading thus eliminating forces needed to stretch, deflect, fold, or otherwise reform the boot configuration. As such, the seal operates with nearly constant sealing force regardless of the length of time in service, or fluctuations in the temperature or hydraulic pressure of the fluid being sealed.
Another advantage of the above seal assembly construction is provided by the flanged tubular insert being molded interiorly of the thickened outer annular portion of the boot in that the tubular portion provides a leak tight and holding radial squeeze in the bore and one of the flanges holds the spring seat at a precise axial position whereat the spring retainer is installed. Because of this the spring seat can be positioned and held axially in respect to the other components of the seal assembly, whereby enabling the spring to achieve an exact and optimum amount of loading regardless of normal axial length variations in the respective components, in each and every seal assembly, regardless of deflected load tolerance in the spring itself.
Another advantage of the above seal assembly is provision of a construction wherein the contoured diaphragm is supported by closely conforming spring retainer and ferrule components, resulting in hydraulic forces being cancelled out because the effective annular area and diameters of the boot subjected to hydraulic pressure effects do not change in area or size with fluctuations in the hydraulic pressure being sealed.
Another advantage of the above seal assembly is a construction wherein the contoured diaphragm is spaced from the frictionally heated seal washer whereby to minimize both stress and heat degradation of the diaphragm in service, possible pinching of the diaphragm, or detrimental scrubbing against the seal.
An advantage of having a metal insert bonded into the seal washer is increased rigidity and dimensional stability of one of the two load bearing members. Extended life of the seal assembly is in part due to the abutting seal faces retaining their flatness, and thus their shape. Additionally, the metal insert can be used to cooperate with the seal washer to form a bearing surface.
An advantage of a seal assembly construction including the locking arrangement between the spring seat and ferrule is a means whereby to limit torsional stresses in the diaphragm and limit the rotational torque acting on the boot without destroying the cross-sectional uniformity of the seal washer. Rotational torque acting on the seal washer is transmitted through the reentrant inner portion of the boot into the ferrule, from the ferrule to the spring retainer, and from the spring retainer into the thickened outer portion of the boot, thus effectively bypassing the contoured diaphragm which connects the annular inner and outer portions of the boot. As a consequence, the fingers and recesses obviate the need for axial recesses in the seal washer itself which destroy its cross-sectional uniformity and thus lower its resistance to leakage causing distortion.
An advantage of a unitized casing in cooperation with the seal seat is provision of a "one-piece assembly" which can be marketed. Specially flaring the casing and deforming the integral shroud after the components have been assembled, respectively, enhances centering of the components and provides a driving engagement of the seal seat. The close fitting but non-distortive back-up positive drive system is easy to fabricate and assembly and has minimal effect on the cross-sectional uniformity of the seal seat component.
In the installed position of a one piece seal washer (or of a seal washer including a metal insert with raised lands spaced angularly), the outermost surfaces of the seal washer are generally exposed to the cooler ambient fluid being sealed in order to enhance removal of frictional heat.
The position of the preloading spring (or springs) can be easily varied during the manufacture of each and every seal assembly to compensate for deviations from the nominal specified combined axial lengths of all components within each and simultaneously compensate for load deviations in the springs themselves.
In another preferred embodiment, the nonrotating assembly includes a seal washer having a sealing face for bearing against a like sealing face from a disk mounted for rotation with the pump shaft, an elastomeric boot having a contoured diaphragm, and a pair of cup-shaped inserts having respective flanges which support the ends of a coil spring disposed therebetween. One of the inserts has an annular wall portion arranged to closely support a part of the diaphragm. The other insert has a cylindrical body sized to press an outer portion of the boot radially outwardly against the bore and a flange to press a portion of the boot axially against an axial end wall of the pump housing. Advantageously, the insert permit use of a spring having a lower force because the inserts do not have to bite into the diaphragm, thereby obviating a situation wherein the boot would be exposed to unnecessarily high stresses.
Although the seal assemblies will be described in detail as they are arranged in a configuration having a bore mounted stationary head portion and a shaft mounted rotating seal seat portion, the seal assembly and its component parts can be configured as one having a shaft mounted rotating seal head portion and a bore mounted stationary seal seat portion without sacrificing any of its inherent advantages.
Further object and advantages residing in the construction, arrangement and combination of features in the structural parts of the seal assemblies in accordance with this invention will become apparent from a consideration of the following detailed description with reference to the accompanying drawings in which: